Transaldolase is essential for maintenance of the mitochondrial transmembrane potential and fertility of spermatozoa

Abstract

Fertility of spermatozoa depends on maintenance of the mitochondrial transmembrane potential (⌬ m), which is generated by the electron-transport chain and regulated by an oxidation-reduction equilibrium of reactive oxygen intermediates, pyridine nucleotides, and glutathione (GSH). Here, we report that male mice lacking transaldolase (TAL) ؊/؊ are sterile because of defective forward motility. TAL ؊/؊ spermatozoa show loss of ⌬m and mitochondrial membrane integrity because of diminished NADPH, NADH, and GSH. Mitochondria constitute major Ca 2؉ stores; thus, diminished mitochondrial mass accounts for reduced Ca 2؉ fluxing, defective forward motility, and infertility. Reduced forward progression of TAL-deficient spermatozoa is associated with diminished mitochondrial reactive oxygen intermediate production and Ca 2؉ levels, intracellular acidosis, and compensatory down-regulation of carbonic anhydrase IV and overexpression of CD38 and ␥-glutamyl transferase. Microarray analyses of gene expression in the testis, caput, and cauda epididymidis of TAL ؉/؉ , TAL ؉/؊ , and TAL ؊/؊ littermates confirmed a dominant impact of TAL deficiency on late stages of sperm-cell development, affecting the electrontransport chain and GSH metabolism. Stimulation of de novo GSH synthesis by oral N-acetyl-cysteine normalized the low fertility rate of TAL ؉/؊ males without affecting the sterility of TAL ؊/؊ males. Whereas TAL ؊/؊ sperm failed to fertilize TAL ؉/؉ oocytes in vitro, sterility of TAL ؊/؊ sperm was circumvented by intracytoplasmic sperm injection, indicating that TAL deficiency influenced the structure and function of mitochondria without compromising the nucleus and DNA integrity. Collectively, these data reveal an essential role of TAL in sperm-cell mitochondrial function and, thus, male fertility. F orward motility and fertility of spermatozoa depend on production of reactive oxygen intermediates (ROIs) (1) and maintenance of the mitochondrial transmembrane potential (⌬ m ) (2, 3). ⌬ m is generated by the electron-transport chain and subject to regulation by an oxidation-reduction equilibrium of ROI, pyridine nucleotides (NADH͞NAD ϩ NADPH͞NADP), and reduced glutathione (GSH) (4). In turn, NADPH, a reducing equivalent required for biosynthetic reactions and regeneration of GSH from its oxidized form, is produced by the pentose phosphate pathway (PPP) (5). The PPP was originally formulated based on metabolites and enzymes detected in yeast (6). Thus, PPP comprises two separate oxidative and nonoxidative phases. Enzymes of the oxidative phase, glucose 6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase, can generate both ribose 5-phosphate (R5P) and NADPH. Although enzymes of the nonoxidative phase, transketolase (TK) and transaldolase (TAL), can convert R5P into glucose 6-phosphate (G6P) for the oxidative phase, and, thus, indirectly, these enzymes can also contribute to the generation of NADPH, the significance of the nonoxidative branch is less well established. Certain organisms (7,8) and mammalian tissu...

Mice overexpression of <i>human augmenter of liver regeneration</i> (hALR) in male germ cells shows abnormal spermatogenesis and reduced fertility

“…ALR/Erv1 catalyzes oxidative protein folding with the generation of disulfides and the reduction of oxygen to hydrogen peroxide, indicating its direct contribution to the oxidative stress. It has been reported that the human spermatozoon is highly susceptible to oxidative stress and disulfide bond formation is a very important issue in sperm physiology leading to a finely regulated redox status, which is needed to stabilize sperm nucleus and tail [33,34]. In addition, ALR performed the export of iron/sulfur (Fe/S) clusters from the mitochondrial matrix, contributing to the biogenesis of cytosolic Fe/S proteins and to cellular iron homeostasis [10].…”

Nitric oxide, mitochondrial hyperpolarization, and T cell activation☆

“…The collapse of Δψ m as a response to pathological states, such as anoxia or as a response to disordered mitochondrial respiration, will limit mitochondrial Ca 2+ uptake and may contribute to cellular pathophysiology [32,34]. Mitochondrial Ca 2+ import is an electrogenic process, as the movement of Ca 2+ is not countered by any other ion exchange and therefore acts like an inward current, tending to depolarize the mitochondrial membrane through increasing the permeability of the voltage-dependent anion channel (VDAC) [35].…”

The pathogenesis of transaldolase deficiency

“…Unlike G6PD and TK deficient mice which are not viable (25,26), heterozygous (TALþ/7) or homozygous (TAL7/7) TAL-deficient mice developed normally with the exception of sperm dysmotility and infertility due to the loss of Dc m (27). TAL7/7 spermatozoa show loss of Dc m and mitochondrial membrane integrity due to diminished NADPH, NADH, and glutathione.…”

“…Complete TAL deficiency also resulted in marked accumulation of S7P in the testis of TAL7/7 mice (27). S7P is a substrate of the forward reaction of TAL that generates G6P for NADPH production by enzymes of the oxidative phase of the PPP (Fig.…”

“…Unlike G6PD-and TK-deficient mice which are not viable (25,26), TALþ/7 or TAL7/7 mice developed normally with the exception of sperm dysmotility and infertility due to the loss of Dc m (27). TAL deficiency has been reported in patients with cirrhosis (28,29), a disease of the liver associated with increased apoptosis of hepatocytes (30).…”